Question 835718
If 40% of the people in the community use the library in one year, for a sample of 4 people find: 

X~Binomial(4, 0.4)
i) The probability that at least 3 used the library.
P(X ≥ 3) = {{{sum( (matrix(2,1,4,x))(0.4^x)(0.6^(4-x)), x = 3, 4 )}}} = {{{highlight(0.1792)}}}

ii) The mean number of library users. 
mean, E(X) = np = 4(0.4) = {{{highlight(1.6)}}}

iii) The variance of the number of library users
variance, Var(X) = npq = 4(0.4)(0.6) = {{{highlight(0.96)}}}